The sensor is S1 in this alarm that we found in a Radio Electronics magazine from May 1971. Several sensors can be used in series. The SCR supports equivalents from the 106 series.
With this circuit, obtained from an American publication for radio amateurs in 1976, it is...
Small variations in the resistance of the skin of a person holding the electrodes can be detected by...
This circuit was found in a 1967 American documentation. The circuit uses components of the time,...